Postfix requires this file to be converted into a '.db' file (in the same directory), to do this simply:

postmap /mail/addresses

This will generate file /mail/addresses.db. Now you need to set the MX record for the domain(s) to the hostname of your mail server. Once this is done try sending a test email and it should forward correctly. Watching /var/log/mail.info will show you it's progress once it hits the server.

Dovecot SASL Setup

The first step to enabling authentication over SMTP/Postfix is to setup Dovecot. We only need a very simple Dovecot setup as the only feature we're going to be using is it's auth server. Dovecot's configuration is in /etc/dovecot/dovecot.conf, we can ignore this file and head to /etc/dovecot/conf.d, where each .conf file is included automatically. I just removed all the files except logging, ssl and auth main. Add the following at the end of auth:

Testing

Restart Postfix and fire up a terminal. Telnet can be used to test a non-secure connection, which will reject auth attempts as per the above config (change smtpdtlsauthonly to no to test auth over Telnet). We can use openssl sclient to test the secure connection with auth: